Field of the Invention
Because of the wide exposure of human epidermis to sunlight for cosmetic reasons or as an employment environment, numerous compositions have been developed which protect the skin from the painful erythemal response. The primary materials which are used are either ultraviolet absorbers (sunscreens) and/or ultraviolet scatterers. With both of these materials, the skin is substantially prevented from tanning or burning while there is a sufficient amount of the material present, but remains unprotected once the material has been removed. Therefore, tanning occurs as a result of partial or no protection during the periods when insufficient amounts or none of the sunscreen is available.
It would be desirable to have a compound which would provide a degree of regulated protection. That is, a compound which will increase the amount of protection as the amount of sunlight intensity increased. Also, higher substantivity is desirable. By substantivity is intended retention of the material by the skin during normal usage of the sunscreen. Also, it is of value to provide compounds which allow for greater synthetic flexibility in varying the compounds as to their lipophilic/hydrophilic balance (HLB) to allow for greater flexibility in preparing formulations for application to the skin, such as solutions, creams, ointments, aerosols and the like.